/*
 * Copyright (c) 2018, apexes.net. All rights reserved.
 *
 *         http://www.apexes.net
 *
 */
package net.apexes.commons.lang;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;

/**
 * 对int值做skip32加密
 *
 * @author <a href="mailto:hedyn@foxmail.com">HeDYn</a>
 */
public class Skip32 {
    
    public static long encrypt(int value, String key) {
        return skip32(value, verifyKey(key), true);
    }
    
    public static int decrypt(long value, String key) {
        return (int)skip32(value, verifyKey(key), false);
    }
    
    private static String verifyKey(String key) {
        Checks.verifyNotNull(key, "key");
        if (key.length() != 10) {
            throw new IllegalArgumentException("The key length must equal to 10.");
        }
        return key;
    }
    
    private static long skip32(long number, String key, boolean encrypt) {
        ByteBuffer buffer = ByteBuffer.allocate(8);
        buffer.order(ByteOrder.LITTLE_ENDIAN);
        buffer.putLong(number);
        byte[] b = buffer.array();
        int[] a = new int[b.length];
        for (int i = 0; i < b.length; i++) {
            a[i] = b[i] & 0xFF;
        }
        
        int[] buf = new int[4];
        System.arraycopy(a, 0, buf, 0, 4);
        
        int[] k = new int[10];
        for (int i = 0; i < k.length; i++) {
            k[i] = key.codePointAt(i);
        }
        
        skip32(k, buf, encrypt);
        
        int index = 0;
        int firstByte = (0x000000FF & buf[index]);
        int secondByte = (0x000000FF & buf[index + 1]);
        int thirdByte = (0x000000FF & buf[index + 2]);
        int fourthByte = (0x000000FF & buf[index + 3]);

        return ((long) fourthByte << 24 | thirdByte << 16
                | secondByte << 8 | firstByte) & 0xFFFFFFFFL;
    }
    
    private static void skip32(int[] key, int[] buf, boolean encrypt) {
        int k;
        int i;
        int kstep;
        int wl, wr;
        
        if (encrypt) {
            kstep = 1;
            k = 0;
        } else {
            kstep = -1;
            k = 23;
        }
        
        wl = ((buf[0] << 8) + buf[1]);
        wr = ((buf[2] << 8) + buf[3]);
        
        for (i = 0; i < 24 / 2; ++i) {
            wr ^= g(key, k, wl) ^ k;
            k += kstep;
            wl ^= g(key, k, wr) ^ k;
            k += kstep;
        }
        
        buf[0] = (wr >> 8);
        buf[1] = (wr & 0xFF);
        buf[2] = (wl >> 8);
        buf[3] = (wl & 0xFF);
    }
    
    private static int g(int[] key, int k, int w) {
        int g1, g2, g3, g4, g5, g6;
        
        g1 = ((w >> 8) & 0xff);
        g2 = (w & 0xff);
        
        g3 = (F[g2 ^ key[(4 * k) % 10]] ^ g1);
        g4 = (F[g3 ^ key[(4 * k + 1) % 10]] ^ g2);
        g5 = (F[g4 ^ key[(4 * k + 2) % 10]] ^ g3);
        g6 = (F[g5 ^ key[(4 * k + 3) % 10]] ^ g4);
        
        return ((g5 << 8) + g6);
    }
    
    private static final int[] F = new int[]{
            0xa3, 0xd7, 0x09, 0x83, 0xf8,
            0x48, 0xf6, 0xf4, 0xb3, 0x21, 0x15, 0x78, 0x99, 0xb1, 0xaf, 0xf9,
            0xe7, 0x2d, 0x4d, 0x8a, 0xce, 0x4c, 0xca, 0x2e, 0x52, 0x95, 0xd9,
            0x1e, 0x4e, 0x38, 0x44, 0x28, 0x0a, 0xdf, 0x02, 0xa0, 0x17, 0xf1,
            0x60, 0x68, 0x12, 0xb7, 0x7a, 0xc3, 0xe9, 0xfa, 0x3d, 0x53, 0x96,
            0x84, 0x6b, 0xba, 0xf2, 0x63, 0x9a, 0x19, 0x7c, 0xae, 0xe5, 0xf5,
            0xf7, 0x16, 0x6a, 0xa2, 0x39, 0xb6, 0x7b, 0x0f, 0xc1, 0x93, 0x81,
            0x1b, 0xee, 0xb4, 0x1a, 0xea, 0xd0, 0x91, 0x2f, 0xb8, 0x55, 0xb9,
            0xda, 0x85, 0x3f, 0x41, 0xbf, 0xe0, 0x5a, 0x58, 0x80, 0x5f, 0x66,
            0x0b, 0xd8, 0x90, 0x35, 0xd5, 0xc0, 0xa7, 0x33, 0x06, 0x65, 0x69,
            0x45, 0x00, 0x94, 0x56, 0x6d, 0x98, 0x9b, 0x76, 0x97, 0xfc, 0xb2,
            0xc2, 0xb0, 0xfe, 0xdb, 0x20, 0xe1, 0xeb, 0xd6, 0xe4, 0xdd, 0x47,
            0x4a, 0x1d, 0x42, 0xed, 0x9e, 0x6e, 0x49, 0x3c, 0xcd, 0x43, 0x27,
            0xd2, 0x07, 0xd4, 0xde, 0xc7, 0x67, 0x18, 0x89, 0xcb, 0x30, 0x1f,
            0x8d, 0xc6, 0x8f, 0xaa, 0xc8, 0x74, 0xdc, 0xc9, 0x5d, 0x5c, 0x31,
            0xa4, 0x70, 0x88, 0x61, 0x2c, 0x9f, 0x0d, 0x2b, 0x87, 0x50, 0x82,
            0x54, 0x64, 0x26, 0x7d, 0x03, 0x40, 0x34, 0x4b, 0x1c, 0x73, 0xd1,
            0xc4, 0xfd, 0x3b, 0xcc, 0xfb, 0x7f, 0xab, 0xe6, 0x3e, 0x5b, 0xa5,
            0xad, 0x04, 0x23, 0x9c, 0x14, 0x51, 0x22, 0xf0, 0x29, 0x79, 0x71,
            0x7e, 0xff, 0x8c, 0x0e, 0xe2, 0x0c, 0xef, 0xbc, 0x72, 0x75, 0x6f,
            0x37, 0xa1, 0xec, 0xd3, 0x8e, 0x62, 0x8b, 0x86, 0x10, 0xe8, 0x08,
            0x77, 0x11, 0xbe, 0x92, 0x4f, 0x24, 0xc5, 0x32, 0x36, 0x9d, 0xcf,
            0xf3, 0xa6, 0xbb, 0xac, 0x5e, 0x6c, 0xa9, 0x13, 0x57, 0x25, 0xb5,
            0xe3, 0xbd, 0xa8, 0x3a, 0x01, 0x05, 0x59, 0x2a, 0x46
    };
    
}
